Preparation And Photocatalytic Activities Of Biobr Hotocatalyst Loaded By Noble Metal (Pt,Au,Ru)

As a promising novel semiconductor photocatalytic material, BiOBr is alayer-structured semiconductor of square matlockite-type (PbFCl) withP4/nmm(No.129) space lattice structure. This structure alternately consists oftetragonal [Bi2O2] layer and two halogen atom-layers, exhibiting uniqueelectronic structures, optical properties and catalytic properties, which haveattracted extensive attention of the researchers. However, the low conductionband position of BiOBr has not enough potential energy to induce the reductionof photoinduced electrons, limiting the photocatalytic degradation efficiency.Therefore, how to modify BiOBr to improve the photo-generated electronreducing ability becomes the key problem to be solved.Noble metal loading can improve photocatalytic properties of BiOBr. Inthis work, we first prepared pure BiOBr by hydrolysis, then the catalyst ofPt/BiOBr, Au/BiOBr and Ru/BiOBr were prepared by UV photoreduction, citricacid reduction and hydrazine hydrate reduction methods. The as-preparedphotocatalysts were investigated by the X-ray diffractometry (XRD), Scanningelectron microscope (SEM), Transmission electron microscope (TEM), X-rayphotoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS) and Photoluminescence spectroscopy (PL) to study on theirstructures, crystallinities, surface compositions and element valences, surfacemorphologies, optical absorption properties. Then, simulated sunlight and UVlight were used as light source to illuminate photocatalysts, MO and phenol inwater were chosen as objective organic pollutants in the photocatalyticdegradation experiments. The obtained results are shown below:(1) A series of Pt/BiOBr photocatalysts were prepared by ultravioletreduction method. The effects of the loading Pt amount, reduction time andreaction time on the photocatalytic performance of BiOBr were discussed. Theoptimum preparation conditions of Pt/BiOBr were the loading amount of0.8%,the reduction time of4h and reaction time of12h. There is no corresponding Ptpeak in XRD spectrum of as-prepared Pt/BiOBr catalyst as a result of littleloading Pt amount on BiOBr. SEM image shows that Pt/BiOBr samples arecomposed of a large number of irregular nanoplates. TEM and HRTEM resultsshow that platinum nanoparticles disperse on the surface of BiOBr. XPS spectrareveals that Pt/BiOBr is constituted by Pt, Bi, O and Br elements. UV-Visspectra of BiOBr occurs slight red shift after loading Pt, which helps to absorbvisible light. PL spectra shows that fluorescence intensity drop after loadplatinum, which enhance photocatalytic activity.(2) A series of Au/BiOBr photocatalysts were prepared by citric acidreduction method. The effects of the loading Au amount, reaction time, reactiontemperature and citric acid concentration on the photocatalytic performance of BiOBr were discussed. The optimum preparation conditions of Au/BiOBr werethe loading amount of0.5%, the reaction time of45min, the reactiontemperature of60oC and citric acid concentration of2g/L. There is nocorresponding Au peak in XRD spectrum of as-prepared Au/BiOBr catalyst as aresult of little loading Au amount on BiOBr. SEM image shows that Au/BiOBrsamples are composed of a large number of irregular nanoplates. UV-Vis spectraof BiOBr occurs slight red shift after loading Au, which helps to absorb visiblelight.(3) A series of Ru/BiOBr photocatalysts were prepared by hydrazinehydrate reduction method. The effects of the loading Ru amount, reaction time,reaction temperature and hydrazine hydrate concentration on the photocatalyticperformance of BiOBr were discussed. The optimum preparation conditions ofRu/BiOBr were the loading amount of0.015%, the reaction time of60min, thereaction temperature of60oC and citric acid concentration of2mol/L. There isno corresponding Ru peak in XRD spectrum of as-prepared Ru/BiOBr catalystas a result of little loading Ru amount on BiOBr.(4) According to the experiments datas and characterization results, wespeculated the mechanism why photocatalytic performance could improve was:noble metal nanoparticles could not only enhance the absorption of incidentlight through Surface Plasmon Resonance effect, but also can restrain thecombination of electrons and holes effectively, then improve the photocatalyticperformance. The recycling experiment results exhibit high stability of as-prepared photocatalysts. The capturing experiments indicated that the mainactive species are holes(h+) and hydroxyl radicals(OH) in this photocatalyticprocess.